Harwood Bridge Upgrade

Soft alluvial soils & slope stability were an issue at the Harwood Bridge site. We provided an engineering solution that helped keep the project on track.
unibridge removal crane construction

Project background

The Pacific Highway Upgrade Project is Australia’s largest regional road infrastructure project. The Woolgoolga to Ballina project (W2B) was the final section of the Pacific Highway upgrade, which completed the upgrade to four lanes between Hexham and the Queensland border.

Building a new bridge over the Clarence River at Harwood was one of the most significant aspects of the W2B upgrade project. The old lift span bridge stopped highway traffic when the bridge was raised, causing long queues to form. The new, upgraded bridge has the height and the grading to end this problem.

Our brief

Acciona, in partnership with Ferrovial, approached Civil Consult back in 2017. The government had awarded them an AU$250 million contract to undertake major works on the Tyndale to Maclean section of the highway upgrade.

Part of that work included the new Harwood Bridge. The Acciona Ferrovial joint venture needed geotechnical engineering consultants to advise on the temporary works design and construction services management.

They asked us to attend the bridge site and assess their proposed ideas on piling and crane platforms. On arrival, we could see straight away that they would need various geotechnical engineering solutions.

The challenge

A significant challenge for the new bridge build was that heavy crane lifts had to take place on the unstable, deep alluvial soft soils that ran alongside the river.

We carried out design calculations and identified that the soil would not be able to accommodate the proposed setups without the use of structurally reinforced working platforms.

This outcome meant we had multiple options to consider. Should we use one giant crane? Or do we bring two? Or three? We evaluated each solution, rejecting the riskier options.

The outcome

We were able to use our geotechnical expertise to advise Acciona Ferrovial that we could manage the soil stability issues through the selection of appropriately designed working platforms that were suitable for the girder lifting crane.

The recommended option was to use a 750-tonne crawler crane in super-lift configuration to raise the girders weighing 176 tonnes each. The construction team lifted each girder 30 metres into position from the working platforms designed and certified by our geotechnical engineers.

Soft soil instability was a significant hurdle on the construction site. And it could have held up the project. The speed of our engineering solution meant that the construction team could get back to work straight away, saving a significant amount of time, money and stress.

The new Harwood Bridge

The new 1.5 km bridge is now in operation and sits 25 metres east of the existing bridge. Building the bridge in this location has several benefits.

First, it minimised the need for new site clearance, which would have reduced the amount of sediment around the bridge and had a long-term effect on the degradation of the riverbed.

Second, the piers of the new bridge mimic those of the old, which has helped to lessen the impact on marine traffic.

The W2B upgrade will have a considerable impact on the Northern Rivers over the coming years. It will contribute to regional growth, road safety and efficiencies in freight movements, not to mention shorter travel times.

unibridge structural engineering and temporary works design including girder proping

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